An automatic transmission of a vehicle includes an input shaft and an output shaft. The input shaft receives an input torque at an input speed from power derived from a power source, such as an engine. The transmission converts the input torque at the input speed to an output torque at an output speed. The output shaft transmits the output torque at the output speed to traction wheels of the vehicle in order to propel the vehicle.
The transmission converts the input torque at the input speed to the output torque at the output speed by adjusting a gear ratio (for example, during an up-shift or down-shift) between the input and output shafts. Transmission shifting is accomplished by applying and/or releasing friction elements (such as clutches, band-brakes, etc.) to change speed and torque relationships by altering planetary gear configurations of the transmission. As a result, power flow paths are established and disestablished from the engine to the wheels.
The friction elements must be properly controlled in order to satisfactorily shift the transmission. To this end, information regarding the operation of the transmission is used to control the friction elements. For instance, information indicative of the input torque received by the input shaft and the speed of the input shaft and information such as vehicle speed and throttle opening may be used. Similarly, information indicative of the output torque transmitted by the output shaft and the speed of the output shaft may be used.